1. Field of the Invention
The present invention relates to a lamp device using an LED, and more specifically, to a spotlight illuminating device using a white LED provided inside a vehicle.
2. Description of the Related Art
There are various kinds of illumination in a vehicle such as wide range illumination by a room lamp and illumination for a step part from a light source provided at a door or the like. These kinds of illumination are mainly necessary for example for securing safety at the time of getting in and out of the vehicle, reading a map, and operating audio equipment. In recent years, LEDs have come to replace light bulbs and fluorescent lamps as light sources for these purposes (see for example JP-UM-A-03-77307 and JP2003-95016A).
In a related illuminating device using an LED for a light source, an LED that emits white light suited for the illumination purpose is used. There are different ways of obtaining white light using LEDs. In one way, light components from light emitting elements for three primary colors, red, blue, and green are mixed. In another way, blue light from a light emitting element for blue and yellow fluorescent light excited by the blue light are mixed. Alternatively, fluorescent light components in three primary colors, red, blue, and green excited by ultraviolet light emitting element are mixed.
Among these methods, the method of mixing luminescent color from a blue light emitting element and fluorescent luminescent color from a fluorescent material is extensively utilized for obtaining white light because the method requires only a single light source and a single fluorescent material.
When white light obtained by mixing the luminescent color from the blue light emitting element and the fluorescent luminescent color from the yellow fluorescent material is converged into a spot for illumination using a lens, there is difference in the light emitting wavelength between the blue-based light and the yellow to yellow-green-based light, and the irradiation range varies depending on refraction. Consequently, color irregularity such as yellow noticeable particularly around the periphery of the illumination light is caused, and homogeneous fine quality light as illumination light cannot be obtained. Meanwhile, in the LED structure using a blue light emitting element and a yellow fluorescent material, the ratio of light converted into yellow by the fluorescent material is different between immediately above the light emitting element and the periphery depending on the optical paths before radiation, and the color irregularity is observed in the illumination light, which is a disadvantage caused by the structure.